1. Field of the Invention
The present invention relates to multifunctional optical devices capable of switching among plural functions with an actuator, and more particularly to pickup devices for performing writing/reading onto or from plural optical disks such as CDs or DVDs.
2. Description of the Related Art
In recent years, an optical device 100 as illustrated in FIG. 10 has been employed in optical pickup devices for CDs or DVDs. The optical device 100 includes a rectangular-shaped base member 102. A fixed-lens holding wall 106 which holds a fixed lens 104 is stood up from a single edge portion of the base member 102.
On the fixed-lens holding wall 106, there is secured a weight 110 of a piezoelectric actuator 108, wherein the weight 110 has, for example, a cylindrical shape. The piezoelectric actuator 108 is constituted by the aforementioned weight 110, a piezoelectric device 112, which is an electro-mechanical transducer secured to the weight 110 at its one end in the direction of extension and contraction, and a driving shaft 114 having, for example, a round-bar shape which is secured to the other end of the piezoelectric device 112 in the direction of extension and contraction. The driving shaft 114 is slidably supported by being passed through supporting walls 106 and 118 which are stood up from the base member 102 such that they are spaced apart from each other by a predetermined distance. The piezoelectric device 108 extends or contracts when a voltage is applied thereto from a driving circuit which is not illustrated.
The optical device 100 includes a movable member 122 holding a movable lens 120. A wedge-shaped cutout portion 124 is formed at one end of the movable member 122, and the cutout portion 124 is engaged with the outer peripheral surface of the driving shaft 114 of the piezoelectric actuator 108. A frictional member 126 is provided to pinch the driving shaft 114 in cooperation with the cutout portion 124 of the movable member 122. The frictional member 126 is coupled to the movable member 122 through an elastic member such as a coil spring or a flat spring which is not illustrated. Thus, the movable member 122 is biased toward the driving shaft 114 through the biasing force of the elastic member, thereby frictionally engaging with the driving shaft 114 with a predetermined frictional force.
A U-shaped cutout portion 128 is formed at the end portion of the movable member 122 which is opposite from the cutout portion 124, with the movable lens 120 positioning therebetween. A straight restricting member 130 having a round-bar shape, for example, is loosely fit in the cutout 128. The restricting member 130 is secured to the fixed-lens holding wall 106 and a guide-member supporting wall 132 at the both end portions thereof in parallel with the driving shaft 114 of the piezoelectric actuator 108. Since the restricting member 130 is fit in the cutout portion 128, the movable member 122 is restrained from rotating about the driving shaft 114 of the piezoelectric actuator 108.
In the optical device 100 having the aforementioned configuration, the movable member 122 is driven along the optical axis by the piezoelectric actuator 108 at the state where the optical axis of the movable lens 120 is always in coincidence with the optical axis L of the fixed lens 104.
Subsequently, the principle of the driving of the piezoelectric actuator 108 will be described. FIG. 11 illustrates respective states of when the piezoelectric device 112 extends and contracts a single time. For example, a triangular-waveform pulse voltage having mild rising-up portions and steep falling-down portions is applied to the piezoelectric device 112, the piezoelectric device 112 repeats slow extension and rapid contraction and thus oscillates.
FIG. 12 illustrates the displacement of the driving shaft 114 of when the piezoelectric device 112 repeatedly extends and contracts. This shaft displacement is generated along a so-called sawtooth profile having mild rising-up portions and rapid falling-down portions, wherein the respective states D, E and F correspond to the states D, E and F in FIG. 11. Assuming that the state D is an initial state, when the piezoelectric device 112 slowly extends, the driving shaft 114 and the movable member 122 which are frictionally engaged with each other are displaced together to the state E at a relatively low velocity. Subsequently, when the piezoelectric device 112 rapidly contracts, the displacement of the driving shaft 114 is restored to the original position at a relatively high velocity, which generates slippage between the movable member 122 and the driving shaft 114, thus causing the movable member 122 to slightly return and reach the state F. At the state F, the position of the movable member 122 has been slightly displaced in the direction of proceeding (namely, in the direction away from the piezoelectric device 112). Since the aforementioned extension and contraction of the piezoelectric device 112 are repeated, the movable member 122 is driven in the direction of proceeding along the driving shaft 114.
On the other hand, the movable member 122 is driven in the direction of returning (namely, in the direction towards the piezoelectric device 112) along the driving shaft 114 on the principle opposite to the aforementioned principle. Namely, when the piezoelectric device 112 repeats rapid extension and slow contraction, the displacement of the driving shaft 114 occurs along a sawtooth profile having steep rising-up portions and mild falling-down portions, on the contrary to that illustrated in FIG. 12. Thus, when the piezoelectric device 112 rapidly extends, slippage is generated between the movable member 122 and the driving shaft 114 while when the piezoelectric device 112 slowly contracts, the movable member 122 and the driving shaft 114 are displaced together in the direction of returning. Since this is repeated, the movable member 122 is moved in the direction of returning.
In a CD/DVD optical pickup device employing the aforementioned optical device 100, the movable lens 120 can be positioned at plural predetermined positions within the range of the driving stroke of the movable member 122 to perform aberration corrections for a laser having plural wavelengths, which enables coping with plural recording mediums with a single optical system.
For example, in FIG. 10, the movable member 122 is finely positioned near the position of the arrow A to perform aberration corrections for a blue DVD laser, the movable member 122 is finely positioned near the position of the arrow B to perform aberration corrections for a red DVD laser and the movable member 122 is finely positioned near the position of the arrow C to perform aberration corrections for a CD laser.
However, as miniaturization and accuracy improvement of optical pickup devices have been advanced, it has increasingly become difficult to perform aberration corrections for a laser having plural wavelengths with a single optical device.
Namely, with advancing miniaturization of optical systems, the tolerances which can secure the optical performance have been reduced below the manufacturing tolerances of conventional optical systems and the assembling tolerances of optical devices. Therefore, there has been a need for establishment of new manufacturing methods and new assembling methods. In order to establish such new methods, enormous amounts of investments are required. Furthermore, even if such methods can be established, the cost of optical devices will be unavoidably increased.
Therefore, it is an object of the present invention to provide optical devices which enable performing aberration corrections with high accuracy for light rays having plural wavelengths, in a simple configuration where no cost increases.